The present disclosure relates to the subject matter disclosed in International Application No. PCT/EP99/05129 (WO 00/08728) of Jul. 19, 1999, the entire specification of which is incorporated herein by reference.
The invention relates to a laser amplification system, comprising a solid-state body having a laser-active medium, a pumping radiation source for generating a pumping radiation field which passes through the solid-state body several times, an optical pumping radiation imaging means which is arranged between the pumping radiation source and the solid-state body and focuses a leg of the pumping radiation field entering the solid-state body onto the solid-state body, and at least one optical refocusing means which focuses a leg of the pumping radiation field exiting from the solid-state body onto the solid-state body again in the form of a leg entering the solid-state body and different to the outgoing leg.
A laser amplification system of this type is known, for example, from EP 0 632 551. With this laser amplification system the leg exiting from the solid-state body is merely deflected and refocused onto the solid-state body.
The disadvantage of such an optical refocusing means consists in the fact that with it the cross section of the pumping radiation field to be focused is always increased in size or considerable losses occur as a result of the fact that part of the pumping radiation field is not refocused onto the solid-state body again. Altogether, it is a problem to achieve as high a pumping radiation power density as possible in the solid-state body, in particular, under the premise that as many passes of the pumping radiation field as possible are aimed for since the absorption of the laser-active medium in the solid-state body is low with a single pass of the pumping power.
The object underlying the invention is therefore to improve a laser amplification system of the generic type in such a manner that as high a pumping radiation power density as possible can be generated in the solid-state body with as little resources as possible.
This object is accomplished in accordance with the invention, in a laser amplification system of the type described at the outset, in that the optical refocusing means reshapes the leg exiting from the solid-state body into an intermediately collimated leg and reshapes the intermediately collimated leg into a leg entering the solid-state body again and focused onto it.
The advantage of the inventive solution is to be seen in the fact that it is possible, as a result of an intermediately collimated leg being generated, to keep the diameter of the pumping light spot approximately the same size, despite refocusing, without the optical element required for the focused leg of the optical refocusing means needing to be adapted to a large beam cross section. In addition, the imaging quality during the refocusing can also be kept essentially constant.
It is particularly favorable when the pumping radiation field passes through several optical refocusing means in series one after the other since their advantages with respect to the imaging quality then become particularly evident, especially with a view to an essentially constant, maximum cross section of the pumping radiation field with an essentially equal pumping radiation spot diameter.
Purely in principle it would be conceivable with the provision of several optical focusing means not only to pump one solid-state body but rather to pump several solid-state bodies therewith.
The inventive advantages become particularly clearly evident when the incoming legs of the several optical refocusing means enter the same solid-state body so that it is, in particular, possible to pump the laser-active medium in one and the same solid-state body in the case of an essentially constant pumping radiation spot diameter with one and the same pumping radiation field under optimum utilization of the power of the pumping radiation source.
This may be realized particularly favorably when the legs entering the same solid-state body enter the same volume area of the solid-state body so that, using the fact that a constant pumping radiation spot diameter may be generated, a volume area corresponding in cross section to this pumping radiation spot diameter can also be pumped several times by the several optical refocusing means and thus a particularly high exploitation of the pumping radiation power is ensured.
One embodiment of the inventive laser amplification system which can be realized particularly favorably, especially from a geometrical point of view, provides for each optical refocusing means to reshape the leg of the pumping radiation field exiting from the solid-state body to form a first partial leg of the intermediately collimated leg, to reshape this first partial leg into a second partial leg of the intermediately collimated leg extending next to it and to form the leg entering the solid-state body from the second partial leg.
The optical refocusing means may be constructed particularly favorably with respect to the space required due to such a folding of the intermediately collimated leg into two partial legs.
Such a folding of the intermediately collimated leg may be achieved particularly favorably when each optical refocusing means has a deflection element for imaging the first partial leg of the intermediately collimated leg into the second partial leg thereof.
With respect to the additional design of the optical refocusing means no further details have been given. One advantageous embodiment, for example, provides for each optical refocusing means to have a collimating element for imaging the outgoing arm into the intermediately collimated leg. This means that the imaging of the outgoing leg into the intermediately collimated leg can be realized in a simple manner.
Furthermore, an additional embodiment provides for each optical refocusing means to have a focusing element for imaging the intermediately collimated leg into the leg entering the solid-state body.
Purely in principle it would be possible with the inventive solution to carry out the pumping of the solid-state body such that the pumping radiation source passes through the solid-state body each time free from reflection when passing from one optical refocusing means to the other optical refocusing means.
A particularly favorable configuration can, however, be achieved when a reflector is associated with a flat side of the solid-state body and the outgoing leg results due to reflection of the incoming leg at the reflector since, in this case, a twofold pumping of the solid-state body is already brought about due to the reflection.
With respect to the alignment of the individual legs in relation to the reflector no further details have so far been given. Particularly favorable conditions may be achieved when a partial leg of the intermediately collimated leg of each optical refocusing means extends parallel to a normal line to a reflection surface of the reflector.
Even more favorable imaging conditions may be created when both partial legs of the intermediately collimated leg of the optical refocusing means extend parallel to the normal line.
A leg of the pumping radiation field entering the solid-state body and the outgoing leg thereof resulting due to reflection of the leg at the reflector define a plane extending through the normal line to the reflection surface of the reflector.
The optical refocusing means are preferably designed with such a solution such that the leg of each optical refocusing means exiting from the solid-state body and the leg thereof entering the solid-state body are located in different planes extending through the normal line.
With respect to the arrangement of the collimating elements of the optical refocusing means no particular details have so far been given. One advantageous embodiment, for example, provides for the collimating elements of all the optical refocusing means to be arranged around the normal line.
In this respect, it is preferably provided for the collimating elements of all the optical refocusing means to be arranged at the same radial distance around the normal line.
Furthermore, it is particularly advantageous for the collimating elements of consecutive optical refocusing means to be arranged at the same angular distances around the normal line.
A solution which is particularly favorable with respect to the optical quality of the refocusing provides for the collimating elements of all the optical refocusing means to be of an identical design.
In the same way it is preferably provided with respect to the focusing elements for the focusing elements of all the optical refocusing means to be arranged around the normal line.
In this respect, it is particularly favorable when the focusing elements of all the optical refocusing means are arranged at the same radial distances around the normal line.
With respect to the angular distances it is likewise advantageous when the focusing elements of consecutive optical refocusing means are arranged at the same angular distances around the normal line.
It is particularly favorable when the focusing elements of all the optical refocusing means are of an identical design.
With respect to the design of the collimating elements in particular, no further details have so far been given. It would be conceivable, for example, to use lenses as collimating elements. A particularly favorable construction may be achieved when the collimating elements are formed by hollow mirrors.
It is particularly expedient when mirrors which are parabolic in cross section or circular in cross section are used as hollow mirrors.
These mirrors could, in principle, be designed such that they generate a line focus.
It is, however, particularly favorable when the hollow mirrors are designed such that they essentially generate a point focus.
A particularly advantageous form of the collimating elements provides for these to be formed by segments of a rotationally symmetrical mirror, wherein the mirror is preferably designed to be rotationally symmetrical to the normal line to the reflection surface.
No further details have likewise been given with respect to the focusing elements. In principle, it would also be conceivable to design the focusing elements as lenses. In this respect, as well, hollow mirrors, in particular, have proven to be advantageous.
The hollow mirrors are expediently designed as mirrors parabolic or circular in cross section.
It would also be conceivable with respect to the hollow mirrors to use those which generate a line focus. It is, however, particularly favorable when the focusing elements are formed by segments of a rotationally symmetrical mirror, wherein the rotationally symmetrical mirror is preferably designed so as to be likewise rotationally symmetrical to the normal line to the reflection surface.
No further details have so far been given with respect to the focal distance of the collimating elements and the focusing elements. It would, in principle, be conceivable to use different focal distances. It has, however, proven to be particularly expedient when all the collimating elements of the optical refocusing means have the same focal distance.
Furthermore, it has proven to be advantageous when all the focusing elements of the optical refocusing means have the same focal distance.
A particularly favorable solution provides for not only the collimating but also the focusing elements of all the optical refocusing means to have the same focal distance.
A solution which is expedient with respect to the production and adjustment of the collimating and focusing elements provides for the collimating elements and the focusing elements of all the optical refocusing means to be formed by segments of a single rotationally symmetrical hollow mirror. In this case, it would, however, also be conceivable to arrange the individual segments so as to be inclined or tilted relative to one another.
A solution is therefore more simple, with which the collimating elements and the focusing elements of all the optical refocusing means are formed by segments of a single rotationally symmetrical hollow mirror with a continuous mirror surface so that not only the collimating elements but also the focusing elements have the same alignment relative to the axis of rotation of the rotationally symmetrical hollow mirror, in particular, to the normal line to the reflection surface of the reflector.
With respect to the arrangement of the deflection elements of all the optical refocusing means no further details have as yet been given. One advantageous embodiment, for example, provides for the deflection elements of all the optical refocusing means to be arranged around the normal line.
In this respect, it is preferably provided for the deflection elements of all the optical refocusing means to be arranged at the same radial distances around the normal line.
A particularly favorable solution from a geometrical point of view provides for the deflection elements of consecutive optical refocusing means to be arranged at the same angular distances around the normal line.
A particularly favorable solution from a constructional point of view provides for the deflection elements of all the optical refocusing means to be of an identical design.
With respect to the relative arrangement of the collimating element and the focusing element of each of the optical refocusing means no further details have so far been given. It would, for example, be conceivable to select the distances between the collimating elements and the focusing elements as required. However, particularly favorable imaging conditions may be achieved when the distance between the collimating element and the focusing element of each optical refocusing means corresponds essentially to the sum of their focal distances. It is particularly advantageous, in particular, in the case of equal focal distances when the distance between the collimating element and the focusing element is approximately double the focal distance thereof.